Due to the increasing need, various flat panel display devices have been developed. For example, the flat panel display devices may be Liquid Crystal Display devices (LCD), Plasma Display Panel (PDP) devices, Electro Luminescence Display (ELD) devices, and Vacuum Fluorescent Display (VFD) devices. Among these flat panel display devices, usually the LCD device is used since it has thinner shape, lighter weight and lower energy consumption. For example, the LCD device is usually used as a substitution for a Cathode Ray Tube (CRT). In addition, the LCD device is usually used in a notebook computer, a computer display and a television. However, in order to use the LCD device in a common display device, the LCD device has to generate an image with high quality, such as a high resolution, a high brightness and a large screen size, while maintaining its lighter weight, thinner shape and lower energy consumption.
FIG. 1 is a cross-sectional view of a liquid crystal cell in the prior art. The liquid crystal cell includes a first substrate 101 and a gate electrode 103 formed on the first substrate 101 and having the shape shown in FIG. 1; and a passivation layer 104 and a first overcoat layer 107 are sequentially formed on the surface of the gate electrode 103. In addition, the liquid crystal cell further includes a second substrate 102 bonded with the first substrate 101, and a black matrix layer 105 and a color filter layer 106 having the shapes shown in FIG. 1 are sequentially formed on the surface of the second substrate 102, and a second overcoat layer 108 is formed on the surface of the color filter layer 106. As shown in FIG. 1, the LCD device is divided into a first region X and a second region Y along a vertical axis. A first spacer 109a is formed on the surface of the second overcoat layer 108 in the first region X, and a second spacer 109b is formed on the surface of the second overcoat layer 108 in the second region Y. The length of the first spacer 109a is greater than the length of the second spacer 109b, and the area of a lower surface of the first spacer 109a is less than the area of an upper surface of the first spacer 109a and the area of a lower surface of the second spacer 109b is less than the area of an upper surface of the second spacer 109b. Furthermore, a liquid crystal layer 111 is formed between the first substrate 101 and the second substrate 102.
As shown in FIG. 2, when a normal pressure (i.e., 300-400 N) is applied to the second substrate 102, the height of a space between the first substrate 101 and the second substrate 102 is reduced, and the length of the first spacer 109a is reduced. When the pressure is removed, the liquid crystal cell can recover to the state shown in FIG. 1 since the first spacer 109a is made of an elastic material.
As shown in FIG. 3, when a greater pressure (i.e., 900-990 N) is applied to the second substrate 102, the first overcoat layer 107 formed on the first substrate 101 suffers pressure from the first spacer 109a and becomes damaged. Furthermore, as shown in FIG. 4, when the pressure applied to the second substrate 102 is removed, the damaged first overcoat layer 107 can not recover.
In order to solve the problem that the liquid crystal cell with the structure described above can not withstand a great pressure, those skilled in the art employ a structure shown in FIG. 5, i.e. both the upper surface areas and the lower surface areas of the first spacer 109a and the second spacer 109b are set to be larger to reduce the intensity of pressure suffered by the first overcoat layer 107. However, employing the technical scheme of FIG. 5 reduces the aperture ratio significantly, which is not beneficial to satisfy the requirements of the modern liquid crystal display with a high resolution.